ComboBox with icons

Each ComboBox item with own icon? No problem. Using OwnerDraw style, we can do almost anything.
Place ComboBox and ImageList on form. Fill ImageList with icons for ComboBox items and set Style of ComboBox to csOwnerDrawFixed or csOwnerDrawVariable. And last thing is the OnDrawItem event of ComboBox:

unit Unit1;

interface

uses
 Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
 Dialogs, ImgList, StdCtrls;

type
 TForm1 = class(TForm)
   ComboBox1: TComboBox;
   ImageList1: TImageList;
   procedure ComboBox1DrawItem(Control: TWinControl; Index: Integer;
     Rect: TRect; State: TOwnerDrawState);
 private
   { Private declarations }
 public
   { Public declarations }
 end;

var
 Form1: TForm1;

implementation

{$R *.dfm}

procedure TForm1.ComboBox1DrawItem(Control: TWinControl; Index: Integer;  Rect: TRect; State: TOwnerDrawState);
var
 ComboBox: TComboBox;
 bitmap: TBitmap;
begin
 ComboBox := (Control as TComboBox);
 Bitmap := TBitmap.Create;
 try
   ImageList1.GetBitmap(Index, Bitmap);
   with ComboBox.Canvas do
   begin
     FillRect(Rect);
     if Bitmap.Handle <> 0 then Draw(Rect.Left + 2, Rect.Top, Bitmap);
     Rect := Bounds(Rect.Left + ComboBox.ItemHeight + 2, Rect.Top, Rect.Right - Rect.Left, Rect.Bottom - Rect.Top);
     DrawText(handle, PChar(ComboBox.Items[Index]), length(ComboBox.Items[index]), Rect, DT_VCENTER+DT_SINGLELINE);
   end;
 finally
   Bitmap.Free;
 end;
end;

end.

Are we connected to the Internet?

Here's how to check whether you are connected to the Internet:

~~~~~~~~~~~~~~~~~~~~~~~~~procedure TForm1.Button1Click(Sender: TObject) ; function FuncAvail(_dllname, _funcname: string; var _p: pointer): boolean; {return True if _funcname exists in _dllname}
var _lib: tHandle;
begin
Result := false;
if LoadLibrary(PChar(_dllname)) = 0 then exit;
_lib := GetModuleHandle(PChar(_dllname)) ;
if _lib <> 0 then begin
_p := GetProcAddress(_lib, PChar(_funcname)) ;
if _p <> NIL then Result := true;
end;
end; { Call SHELL32.DLL for Win < Win98 otherwise call URL.dll }
{button code:}
var InetIsOffline : function(dwFlags: DWORD): BOOL;
stdcall;
begin
if FuncAvail('URL.DLL', 'InetIsOffline', @InetIsOffline) then
if InetIsOffLine(0) = true then
ShowMessage('Not connected')
else
ShowMessage('Connected!') ;
end;
~~~~~~~~~~~~~~~~~~~~~~~~~

Numerical Entry Only On TEdit

If you want to limit the input of a TEdit to numerical strings only, you can discard the "invalid" characters in its OnKeyPress event handler. Let's assume that you only want to allow positive integer numbers. The code for the OnKeyPress event handler is as follows: procedure TForm1.Edit1KeyPress(Sender: TObject; var Key: Char); begin // #8 is Backspace if not (Key in [#8, '0'..'9']) then begin ShowMessage('Invalid key'); // Discard the key Key := #0; end; end; If you also want numbers with a decimal fraction, you must allow a POINT or a COMMA, but only once. For an international version that looks at the correct decimal separator, the code could be as follows: procedure TForm1.Edit1KeyPress(Sender: TObject; var Key: Char); begin if not (Key in [#8, '0'..'9', DecimalSeparator]) then begin ShowMessage('Invalid key: ' + Key); Key := #0; end else if (Key = DecimalSeparator) and (Pos(Key, Edit1.Text) > 0) then begin ShowMessage('Invalid Key: twice ' + Key); Key := #0; end; end; And here's a full blown version of the event handler, accepting a decimal separator and negative numbers (minus sign: only accepted once, has to be the first character):

procedure TForm1.Edit1KeyPress(Sender: TObject; var Key: Char);
begin
 if not (Key in [#8, '0'..'9', '-', DecimalSeparator]) then
   ShowMessage('Invalid key: ' + Key);
   Key := #0;
 end
 else if ((Key = DecimalSeparator) or (Key = '-')) and
         (Pos(Key, Edit1.Text) > 0) then begin
   ShowMessage('Invalid Key: twice ' + Key);
   Key := #0;
 end
 else if (Key = '-') and
         (Edit1.SelStart <> 0) then begin
   ShowMessage('Only allowed at beginning of number: ' + Key);
   Key := #0;
 end;
end;

How about giving that same behaviour to several TEdits on the same form, say 10 of them? In the Object Inspector, you change the name of the event handler of Edit1 from Edit1KeyPress to Edit1_10KeyPress or something similar. Delphi automatically changes the name in the code editor, don't worry.

Then, for each next TEdit, you select its OnKeyPress event and you select Edit1_10KeyPress from the listbox next to the event.

Finally, we have to slightly adapt the code. Intead of pointing to Edit1, we must point to "the TEdit that generated the event", in other words: the edit-box where the cursor was when a key was depressed. When you look at the template for the event handler that Delphi made, you see the parameter Sender: that's a pointer to the component that generated the event. But we are not allowed to use it straight away in our code, we must specify that we're dealing with a component of the type TEdit. That's done with the code Sender as TEdit:

procedure TForm1.Edit1_10KeyPress(Sender: TObject; var Key: Char);
begin
 if not (Key in [#8, '0'..'9', '-', DecimalSeparator]) then
   ShowMessage('Invalid key: ' + Key);
   Key := #0;
 end
 else if ((Key = DecimalSeparator) or (Key = '-')) and
         (Pos(Key, (Sender as TEdit).Text) > 0) then begin
   ShowMessage('Invalid Key: twice ' + Key);
   Key := #0;
 end
 else if (Key = '-') and
         ((Sender as TEdit).SelStart <> 0) then begin
   ShowMessage('Only allowed at beginning of number: ' + Key);
   Key := #0;
 end;
end;